Fertilizer is often applied as a formulated (N—P—K) solid, granular or powder, or sometimes as a liquid to an area to be fertilized. There are basically two types of fertilizers, water soluble fertilizers and “slow release” fertilizers. While water soluble fertilizers are generally less expensive than slow release fertilizers, they have the disadvantage of leaching nutrients very quickly into and through the soil. Some solid, water soluble fertilizers can be made slow release by various coatings. Alternatively, a reduction in nitrogen availability also can be obtained by using enzyme inhibitors. Slow release fertilizers are designed to release nutrients to plants or soil over an extended period of time, which is more efficient than multiple applications of water soluble fertilizers. Therefore, slow release fertilizers (also referred to as controlled release or extended release) minimize the frequency with which plants must be fertilized, as well as reduce or minimize leaching.
Urea-formaldehyde (UF) condensation products are widely used as slow release nitrogen fertilizers in crops, ornamental plants and grasses. Urea-formaldehyde fertilizer materials also can be supplied either as liquids or as solids and are the reaction products of urea and formaldehyde. Such materials generally contain at least 28% nitrogen, largely in an insoluble but slowly available form.
Extended release UF fertilizers (ureaform) can be prepared by reacting urea and formaldehyde at an elevated temperature in an alkaline solution to produce methylol ureas. The methylol ureas then are acidified to polymerize the methylol ureas to methylene ureas, which increase in chain length as the reaction is allowed to continue.
The methylene urea polymers that the condensation products normally contain have limited water solubility and thus release nitrogen throughout an extended period. The mixture of methylene urea polymers generally have a range of molecular weights and are understood to be degraded slowly by microbial action into water soluble nitrogen. UF fertilizers are usually evaluated by the amount and the release characteristics of their water insoluble nitrogen.
U.S. Pat. No. 4,089,899 describes a solid, controlled release nitrogen fertilizer of the ureaform type, which consists essentially of only two nitrogen fractions: water soluble nitrogen and cold water insoluble nitrogen.
U.S. Pat. No. 3,677,736 describes a urea-formaldehyde fertilizer suspension.
Other disclosures of urea-formaldehyde fertilizer compositions, both liquid and solid forms include U.S. Pat. Nos. 4,378,238, 4,554,005, 5,039,328, 5,266,097, 6,432,156, and 6,464,746.
Granular nitrogen-containing fertilizers have been produced commercially by a variety of techniques using water soluble nitrogen products, such as urea, potassium nitrate, and ammonium phosphate. The practical advantages of handling, blending, and storing such fertilizer granules are known and well documented. The preparation of granular fertilizers using slow release UF fertilizers also has been described in the prior art.
The present invention proposes to provide a new source of a particulate slow-release nitrogen (UF) as a plant fertilizer and to use such particles for forming granular fertilizer compositions.